Meteorology

Understanding weather and being able to predict where the next storm will strike is essential to avoid wasted days travelling to non-events or missed opportunities.

Following TV or radio weather forecasts and studying websites, chasers will look out for the key ingredients of a worthy weather pattern: instability, moisture, lifting pressure and rising winds. Warm and cold fronts often loom behind these factors. Chasers will often aim for what is known as 'the dryline', where moist and dry air meet.

When there is an increasing pressure difference between two neighbouring areas the air flows more quickly from the high to the low pressure areas, in the same way as water would flow faster down a steeper hill than a gradual decline. Sea tidal activity can add to this effect, which can be further intensified at the time of the equinoxes when gravity from the sun and the moon unify to form a particularly strong pull on the tide, bringing huge wave swells and catastrophic storms.

At the turn of the 19th century, Sir Francis Beaufort developed the now universally recognised scale for measuring wind speed: the Beaufort Scale. This ranges from 0 (under 1kmh, mirror-like sea, vertically-rising smoke and a World Meteorological Organisation designation of calm) to 12 (73kmh or faster, wide-spread spray at sea, far-reaching damage, hurricane).

Tornadoes can also be classified by the Fujita Scale developed by Professor Fujita and Allen Pearson, director of NSSFC (National Severe Storm Forecast Center). This grades their intensity by examining the damage caused after they have passed over a structure made by man.

F0 in the Fujita Scale is a gale strength of 40-72mph causing damage to chimneys, breaking tree branches and pushing over shallow-rooted trees. An extreme F6 would top 319-379mph and fling cars and refrigerators into the air causing serious damage, although no one is sure whether any tornado has reached this intensity.

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